The exact causes behind dementia are varied and at times unclear. We know that genetic factors — like carrying the APOE4 gene — can have an impact on a person’s risk of developing Alzheimer’s, as can lifestyle or environmental factors like diet, exercise and exposure to air pollution. And a new study adds to the growing evidence that weight and obesity may also contribute to a person’s dementia risk.
The study, conducted by researchers at the University of Oxford in the U.K., was published in Neurology and examined over one million women living in the U.K.
Researchers have known from past studies that a larger waist size, and metabolic issues like diabetes, are linked to neurodegenerative diseases like Alzheimer’s and dementia. But the scientists working on the latest study wanted to examine this connection further.
The goal was to “help determine whether midlife obesity is a cause of dementia” rather than just a correlation. Plus, the researchers wanted to understand why there has appeared to be a link between the development of dementia and low body mass index (BMI), low calorie intake and physical inactivity. Does the dementia cause a person to lose weight and become inactive, or is it the other way around?
Investigating Obesity, BMI and Dementia
The researchers followed over one million women, who had a mean age of 56, for 15 years — from 1996 to 2001. They measured height, weight, caloric intake and levels of physical inactivity. In 2017, the researchers followed up with the women by taking note of their National Health Service records, marking down hospitalizations and any mentions of dementia.
They found that women who were considered obese — with a body mass index (BMI) over 30 — were 21 percent more likely to develop dementia compared to women with a healthier BMI of 20-24.9.
2.2 percent of the women with obesity ended up with dementia long-term, but only 1.7 percent of the women with a healthy BMI did. This suggests that obesity likely contributes to the development of dementia.
Interestingly, however, the researchers found that while the other three factors investigated — low caloric intake, low BMI and inactivity — were associated with a higher dementia risk earlier on in the women’s lives, they ultimately did not appear to contribute to the risk over the long-term.
“Some previous studies have suggested poor diet or a lack of exercise may increase a person’s risk of dementia,” Sarah Floud, lead researcher on the study, said. “However, our study found these factors are not linked to the long-term risk of dementia. The short-term links between dementia, inactivity and low calorie intake are likely to be the result of the earliest signs of the disease, before symptoms start to show.”
However, that’s left to be debated — as many experts and past researchers have argued that a person’s Alzheimer’s or dementia risk is greatly reduced if they eat a healthy diet and exercise. One recent study suggested that up to one-third of dementia cases could be prevented with lifestyle changes.
Floud does agree, however, that obesity is likely tied to a greater dementia risk. “On the other hand, obesity in midlife was linked with dementia 15 or more years later,” she said. “Obesity is a well-established risk factor for cerebrovascular disease. Cerebrovascular disease contributes to dementia later in life.”
The relationship between the metabolic system and dementia is complex and still being investigated by researchers.
However, many experts advocate for their patients to stay active, whether or not they have a risk of developing Alzheimer’s. Exercise has been shown to be the single most effective preventive tool against the disease.